I. Field of the Invention
The present invention relates to safety and service valves for high pressure gas tanks and, in particular, for a new and improved valve for compressed gas tanks which is capable of releasing high pressure gas as desired, but which will shut off the flow of gas in the event of a rupture of the valve and which will maintain the pressure in the tank above a predetermined minimum value.
II. Description of the Prior Art
Compressed gases contain energy that is generally proportional to the pressure and volume of the compressed gas and such compressed gases are capable of performing tremendous amounts of work. Thus the sudden release of a compressed gas, such as during the rupture of the service valve on a high pressure tank, may be very hazardous. The equipment that is used to compress gases to a high pressure is expensive, and it is a common practice to compress the gas to a high pressure at a central location and transport the compressed gas in high pressure tanks. These tanks can be as destructive as a bomb should they rupture because of the high pressure at which thes tanks are maintained, and thus as a safety precaution, there is a common practice to have only one opening in the tanks for permitting access to the gas contained within the tank. These openings are generally small and are threaded to permit the connection of a closure valve or shut-off valve either of which are exceedingly rugged in their construction but nevertheless are weaker than the tank structure itself, and thus if the tanks are accidently dropped or the valve bodies otherwise hit, the valve body may crack off externally from the tank on which it is mounted. The violent release of gas which occurs when the valve bodies are broken produces a tremendous thrust capable of blowing a tank through a solid brick wall. The tremendous hazards which these bottles create has long been recognized, and to guard against this hazard cylinders are shipped with a protective cap; however, these protective caps provide protection only while the cap is on the tank and the tank is being transported. During use the cap must be removed to gain access to the connection of the valve for purposes of utilizing the gases within the tank.
It would therefore be desirable to provide a safety and service valve for high pressure gas tanks which eliminates the aforementioned hazard tha occurs when a tank shut-off valve is inadvertently knocked off the tank on which it is installed. Examples of safety and service valves for high pressure gas tanks are disclosed in U.S. Pat. Nos. 1,525,775, 1,698,616, 2,563,244, 2,765,801, 3,480,183 and 3,648,893.
In certain applications it is necessary that a minimum amount of pressurized gas remain in the tank. This is especially desired in oxygen holding tanks. It would therefore be desirable to provide a safety and service valve for high pressure gas tanks which has all of the advantages described hereinbefore, and one which will prevent the pressure within a gas tank from falling below a predetermined amount.